text:
Where can I find airport taxi instruction "code names"?
At larger airports, common taxi instructions are sometimes "named" for brevity as they are repeated often. For (an entirely contrived) example,

Taxi to terminal via alpha, tango, foxtrot, mike four, sierra

could be shortened to something like

Taxi via red-flower

Where can these common taxi route definitions be found?

if you don't understand the short instruction then you can always ask the controller for the full list

Excerpt from the FAA Publication "Instrument Procedures Handbook":

Standard taxi routes improve ground management at highdensity
  airports, namely those that have airline service. At
  these airports, typical taxiway traffic patterns used to move
  aircraft between gate and runway are laid out and coded.
  The ATC specialist (ATCS) can reduce radio communication
  time and eliminate taxi instruction misinterpretation by
  simply clearing the pilot to taxi via a specific, named route.
  An example of this would be Los Angeles International
  Airport (KLAX), where North Route is used to transition
  to Runway 24L. [Figure 1-7] These routes are issued by
  ground control, and if unable to comply, pilots must
  advise ground control on initial contact. If for any reason
  the pilot becomes uncertain as to the correct taxi route, a
  request should be made for progressive taxi instructions.
  These step-by-step routing directions are also issued if the
  controller deems it necessary due to traffic, closed taxiways,
  airport construction, etc. It is the pilot’s responsibility to
  know if a particular airport has preplanned taxi routes, to
  be familiar with them, and to have the taxi descriptions
  in their possession. Specific information about airports
  that use coded taxiway routes is included in the Notice to
  Airmen Publication (NTAP).

NTAP can be found on: https://www.faa.gov/air_traffic/publications/notices/
At the time of writing the KLAX North Route example can be found on page 4-SW-11, and reads:

North Route
  Taxi towards taxilane Sierra (S) taxi northbound on taxilane Sierra (S), and at Check-point-1 contact Ground
  Control on frequency 121.65, hold short of taxiway Delta (D).
  Taxilane Sierra (S) is not visible from the ATCT

There's also FAA Advisory Circular 7110.116 regulating Standard Taxi Routes (STR's) as bilateral agreements (LOA's - Letter of Agreement) between each ATC unit and their users (airlines). The document contains information on what the LOA needs to contain.
Outside of the US, standard taxi instructions, if any, could be expected to be found in the AD-section (Aerodromes) of that respective country's AIP (Aeronautical Information Publication).
As an airline pilot, this information might be integrated into your company's nav data solution, ie. information about standard taxi routes available to you would be written/drawn out bundled with your airport diagrams etc.

If it's not a taxi-way odd name(Inner/Outer/Dixie, etc) that's on the chart, it's usually a procedure that's in a letter of agreement with the specific airline/companies. I know at Atlanta, there's a Letter of Agreement with some of the airlines(Delta I know for sure, not positive about others and don't have access from home to the repository), where they'll taxi via the Victor loop, which denotes taxi-ways, and when to change to the appropriate ground control frequency.
To find these out, you'd have to be privy to the specific LOA at each airport. Or if you've flown in and out of the airport enough you will often be able to figure them out by watching those privy to the LOA and what they do.


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Why does the chevron-shaped engine suffer losses in thrust performance?
From here I found out a lot about chevrons on the Boeing 787, but not enough to satisfy why it results in performance loss.

My thinking was originally, if they are "cutting triangular holes" in the "bell cone", then some part of the exhaust will expand sooner than others. (I'm more of a rocket guy myself). Or you could think of it as "adding triangular extensions" to the optimal bell-cone, in which case some parts of the exhaust will expand later than usual. Or you could meet in the middle, which is probably the best way, but will still result in suboptimal expansion.
But I find myself wondering about an even simpler analogy: If sound is wasted energy from an engine (that could have gone into thrust), then reducing sound somehow must mean that otherwise wasted energy has actually gone into thrust production and therefor would boost thrust performance?
So which is it really, and why?

I'd assume it'd become heat.

The chevrons need a small pressure difference between the fan flow and the surrounding air. Then they will work like small delta wings and create two strong vortices per triangle, which will help to mix fan flow and outer flow. This mixing is responsible for the reduced noise, because it will distribute the kinetic energy of the fan flow over a bigger mass of air.
This mixing by itself uses up some of the energy of the fan flow, and thrust is produced by the conversion of the pressure increase due to the fan into kinetic energy. With the chevrons, a little of this kinetic energy is now spent for mixing and cannot contribute to thrust anymore. Hence the reduced efficiency.
You're right to assume that less sound should mean more thrust. In fact, the sound energy is not evenly distributed over all frequencies, and by adding some noise at frequencies with low noise contribution, the peaks at the lower frequencies which contain most of the noise can be lowered.

Also keep in mind that sound contains a very very small amount of energy, as shown by http://www.physicscentral.com/explore/poster-coffee.cfm

That's correct; a 94dBSPL sound, roughly equivalent to the sound level of a circular saw as heard by the user, is a pressure wave of about one Pascal pressure difference, which is one Newton per square meter of surface area. The average jet engine produces about 200 Pa in sound level as measured through open air at about 30 meters away, which is instantly deafening. The 787's most powerful engine configuration, for the 787-10, produces 1,700 times that much thrust at the exhaust of each engine.

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How are wood and canvas wings able to sustain damp and bad weather?
Small aircraft have used and still use at least for wings, and perhaps for fuselage, material like wood and canvas, as visible on the bottom side of this wing:

Robin DR400, source: aeroVFR
Which kind of fabric / which treatment are used? What are the limits:

Are such structure able to withstand bad weather, rain, hail...
Refresh periodicity
Maximum wing load / aircraft size

about weather, we have a partial answer here: https://aviation.stackexchange.com/a/19574/1467 <An additional benefit in the war for independence of the Baltic states during 1919 was their robustness - the fast shifting front lines made solid hangars impossible, and wooden airplanes were unusable after rain, so on many days only Junkers airplanes could take to the air.>

The fabric was painted with something called "dope" that made the wings waterproof. Dope is a plasticized lacquer  and you can still buy it for model building.

@zeta-band You can still buy butyrate dope for full sized aircraft.

FAA's Aviation Maintenance Technician Handbook - Airframe has some details about the fabric coverings used in modern aircraft.

Wood and canvas are not meant to be used in humid conditions. All outer surfaces are painted, so they are water repellent and can sustain a shower, but when left to the elements, wooden aircraft deteriorate rapidly. The unprotected structure will take up water and will warp. Wet canvas is less taut, many glues lose strength when wet and plywood will come apart over time. When a wooden aircraft has suffered a shower, it should be wiped dry and stored under a roof as soon as practical.
When Junkers introduced all-metal aircraft, they were sometimes the only types to fly because bad weather had made all other types unusable. In the war for independence of the Baltic states during 1919, the rapidly moving frontline made the use of aircraft hangars impossible, and only Junkers airplanes were able to operate on rainy days.
DeHavilland designed a sleek, four-engined airliner, the DH.91 Albatross, in 1936. The last three of seven built were put out of service after a crash in Shannon in 1943. This crash had made the fact obvious that the plywood structure had deteriorated beyond repair in bad weather, despite a fabric-and-dope cover to protect it from the elements.
The good thing about wood is its long-term strength. In stark contrast to aluminium, wood shows no fatigue under stress and allows to design a life-safe structure. When stored and operated properly, a wooden aircraft will last centuries. While the fabric cover will lose strength over time and needs to be replaced maybe every 20 years, the wooden structure needs no rejuvenation.
The maximum size of wood-and-canvas aircraft was demonstrated by the Caproni Ca.60, and that of wooden aircraft by the Hughes H-4. Both were the biggest aircraft of their time (1921 / 1947) and were bigger than a Jumbo Jet if you use wing area to measure size. However, fabric cover puts a low limit on flight speed, and indirectly on wing loading. The DH.91 had only 134 kg/m² and I would be surprised if any wood-and-canvas aircraft with a wing loading above 200 kg/m² exists. Even the plywood-covered DH.98 Mosquito had only 195 kg/m².
Now to the materials: Otto Lilienthal used osier stakes which he covered with nettle cloth. As far as I know, treatment was wax (applied dissolved in a volatile solvent). Early designs used linen or cotton and dope for glueing the cloth to the structure as well as tightening the cover. Since maybe 50 years those natural fibers have been displaced by polyester cloth because it has less of a tendency to rot. Still dope is used for glueing and tightening, and a finish of synthetic resin lacquer is used as topcoat.

@Pete: Did it had a canvas-covered wing? I changed the label slightly.

One additional point: because aircraft are weight-limited in design, reliability cannot be designed in by oversizing all the critical components. Instead, reliability is inspected in by requiring teardowns at fixed intervals so that material failures and fatigue cracks can be detected before catastrophic failure. This is a perfectly valid engineering approach in a weight-constrained design space.

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What is the origin of the term "pax"?
Pax in commercial transport is used as something like persons or passengers, in the context of counting people, e.g. 150 pax onboard.

(Amadeus capture, source)
I observed that in German writers tend to use the meaning:

PAX = Persons approximately.
(Source: European Union and the Committee of the Regions)

English.SE has a page for What does “pax” mean in the context of the apartment rental? Selected answer:

Pax isn't exactly shorthand for Passengers. It's short for
  Passengers and Passes.

But the author of the answer agreed that another answer was likely more accurate. The latter has a reference to a magazine, Air Facts: The Magazine for Pilots - 1946:

Cargo is known as "cargo", but passengers are called "pax" by the
  traffic department, who puts them on and takes them off the airplane
  and "bodies" by the crews who fly them.

Pax could be from passenger as usually assumed in the Aviation community, albeit I don't see why not *pass" instead. I wouldn't be surprised it comes from the merchant navy.
Can we track the use further back to the origin in aviation field?

Might be better asked on http://english.stackexchange.com where you can inquire about the etymology of certain phrases. I don't think its specific to aviation, pretty much any industry that caters to passengers uses "pax" as an abbreviation, so aviation may just borrow it from an unrelated field.

@mins Would be interesting to know if it was in use during the steamship era too e.g. pre 1920.

@mins A google ngram search is very interesting. "pax" in lower case declined greatly from 1850 till now. On the other hand "PAX" and "Pax" both have been continuously increasing from the 1800's with more recent peaks.

FYI, I am ex-military (air force) and never heard pax used except to mean passenger.

@Simon: ah, thanks. Will correct.

@curious_cat I wonder if some of the uses of pax from 1800s and earlier were related to the Latin word meaning 'peace' (e.g. the "Pax Romana") rather than as an abbreviation for 'passengers' as it's used in aviation?

when I worked in the airline technology business, IATA was the authoritative source of data processing systems. according to IATA, PAX means passenger. you can find lots of references googling 'IATA PAX'

@reirab: Indeed. Looking at the results, the first occurrence I found in the transport field was 1958.

@mins I always assumed it was shorthand in early reservation systems and it just stuck. I know in SABRE RES/DECS everything is shorthand or more often random short codes.

@RonBeyer : I agree with you, this question is suited more for the English SE.

The 'x' suffix is aviation speak in an abbreviated word called a contraction.  You can think of the 'x' as "cut short" shorthand.  Some are defined in manuals or advisory circulars.  For example, WX is weather as defined in an old advisory circular, AC00-45.
Official or not, a few others that come to mind are:

MX - maintenance
CX - cancel
TX - transmit
RX - receive

Maybe others will chime in the comments with more lore. The -x is also used outside of aviation, and is a common abbreviation marker, e.g. Dx ("diagnosis"), elex ("election"), and Hx ("history").

This is the first time I read this explanation which is very plausible, do you have any document that could support it?

Please see the link contraction in my answer, for example.  The right-hand column of that government document shows a source.

Perhaps my answer missed the root of your question, origin being the earliest use.  Having been in aviation my life, cutting words short in log entries and aviation reports with 'x' has been commonly understood.

Rx & Tx are common for Receive & Transmit in the computer world, as well - look at your router/modem & you will, most likely see a light for each.

Related: https://en.wikipedia.org/wiki/X   In abbreviations, it can represent "trans-" (e.g. XMIT for transmit, XFER for transfer), "cross-" (e.g. X-ing for crossing, XREF for cross-reference), "Christ-" as shorthand for the labarum (e.g. Xmas for Christmas, Xian for Christian), the "crys-" in crystal (XTAL), or various words starting with "ex-"

Rx is also short hand for "Prescription" in the medical world, so it's important to know the context!

Pass would not be used as in the old days employees travelled on a 'pass'instead of a ticket. It could also be confused with the verb.
As a side note .. I seem to remember the plural was PAX and singular was PAP... eg 1PAP, 3PAX.


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Does a skinless fuselage add to the likeliness of an unrecoverable spin?
While at Air Venture this week, I happened to hear a pilot of a small experimental airplane say that he liked the skinless (Naked) look his airframe had at one point during the build, but that he believed flying it that way made it more susceptible to an unrecoverable (I assume flat) spin.

Thinking about it later, I realized that I wasn't sure I understood how this could be.  My understanding of airplane behaviour is that a flat spin is mostly a result of CG being to far aft.  Anyway, I was wondering if anyone knew this?

is that a picture you took of the airplane in question, or you randomly picked an image from the internet?

Some kind of transparent skin seems like the best solution?

Well, I would solve with transparent Monokote if it was a model.  No accounting for people's taste.
Although some very early aircraft featured that look, designers soon realized that covered "slab" sides not only reduced drag, but also improved directional stability.  Note that covered area aft of CG acts as an extension of the empennage, allowing for a smaller Vertical stabilizer.  Many 100 years ago were comparitively tiny.
As far as behavior in a spin, what he has on the tail may be sufficient for safety, as well as good CG management.   But I would certainly not recommend denuding your fuselage for a certain "look" without some expert advice and testing.
Designers do compare side area ahead of CG to aft of CG to estimate yawing tendency in a slip.  So he may be OK.

Strictly speaking, yes.
That is not to say the airframe is dangerously unstable in yaw or prone to spinning, only that the tail boom does contribute slightly to tail volume, so, disregarding any weight and balance effects form the fairing and assuming everything else stays the same, the "naked" version will have less lateral stability.
The vertical tail volume coefficient can be defined as:
$$
V_v=\frac{S_v l_v}{Sb}
$$
In the numerator, $S_v$ is the area of the vertical tail and $l_v$ is its moment arm. The denominator contains the wing area ($S$) and span ($b$). Non-tail surfaces are often obviated for simplicity, but a more rigorous expression would be:
$$V_v=\frac{\sum_{i=1}^n S_{v_{i}} l_{v_{i}}}{Sb}$$
where each surface aft of the CG is weighted by its moment arm and added to the coefficient. This would include the boom area.
This coefficient represents the capability of the tail to counteract yaw; a lower value will lead an aircraft that is more prone to yaw, and easier to spin (again, all else being equal).

Susceptibility to spins does depend on CG location, because an aft CG will place the center of rotation closer to the tail, reducing the arm it has to counteract yaw, which translates to less tail volume. In the case of such GA aircraft, the addition of a couple kilograms at most of cloth to the boom structure should not shift the CG out of envelope unless the design is already at its limit.

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text:
What is this flying boat being restored at the Udvar Hazy Center?
I am fortunate to live ~20 minutes from the Smithsonian Steven F. Udvar-Hazy Center.  At the back of the Museum is there restoration hangar, surrounded on two sides by a second level glass enclosed observation walk which allows guests to look in on what is being restored.  Because these aircraft aren't actually on display, I was not able to figure out what type of plane this is:

I was originally thrown off by the wings in the background, clearly embossed with the German Iron Cross, but I don't think the flying boat in the foreground is German.  Can anyone identify the plane in the foreground?
Here's a link to the original photo, in case you want to get a closer look.

MUCH more interesting than some old Sikorsky is the Horten IX in the background!!!

@PeterKämpf it was so stealthy I didn't even see it until you mentioned it!

I'm guessing the wing sections belong to the Horten IX? They look about the right size/shape. Really glad to see it being restored...

This one, I assume?

What reentry vehicle is poking its way into the right frame of the photo? I've gone to the Smithsonian site and searched for the obvious keywords. It looks like an Apollo CM to me.

@IconDaemon Not sure so I've posted the question on space.SE

@IconDaemon It's Apollo 11.

Thanks, all. To see this spacecraft, amidst a few of its precursors in flight, is truly awe inspiring.

It is a Sikorsky JRS-1 (Like terry I thought it was a PBY as well at first glance, that center wing joint is fairly unique)
From the smithsonian website you can find all the info on it here

This amphibious seaplane is the only aircraft in the Museum that was
  at Pearl Harbor, Hawaii, on December 7, 1941. Ten JRS-1s were at the
  U.S. naval base when the Japanese attacked during World War II. The
  Navy immediately sent these unarmed utility craft to search for the
  enemy fleet. The JRS-1 (used 1937-1944) is the military version of the
  Sikorsky S-43 "Baby Clipper." On the day of the attack, the plane wore
  a very colorful paint job: silver overall, black on the bottom, green
  tail surfaces, a red band around the rear of the fuselage, and the
  diamond-shaped squadron insignia behind the cockpit on each side. A
  few days after the attack, ground crew repainted the plane blue, but
  it has weathered and the original paint is peeking through. The
  JRS-1’s current condition is due to many years of storage outside. The
  Museum intends to conserve and restore the plane. Transferred from the
  U.S. Navy, Bureau of Weapons

Good catch! I'm removing my incorrect answer.

Excellent find.  Just curious Dave, do you remember what you clicked from the website to find this?

@bclarkreston I did a search here for everything in the "Restoration Hangar"

There is another Sikorsky flying boat at Windsor Locks, CT, museum...a VS-44A, once owned by Maureen O'Hara and her husband.


text:
What is the difference between side-by-side vs under-cockpit engine intakes?
What is the main difference between these two engine configurations?
What are the differences between planes that have the intakes below the cockpit as compared to those who have them on the sides?
What are the aerodynamic differences?
How does this affect the speed/radar signature/maneuverability of the aircraft?
These two configurations are used for almost every existing type of small military aircraft, be it a fighter, an interceptor, ground attack or a bomber - why so? It would be interesting to know why some aircraft have the configurations that they do.

I wouldn't call the Su-27 small, but that is another issue.
The main difference is the wing planform. The Su-27 wing is optimised to work over all angles of attack up to 120° with very little pitch moment change. This requires the addition of strakes which create vortex lift at higher angles of attack. With this planform the straight side intakes would be impossible. But there is more to it.
At high angles of attack and high transsonic or supersonic speed, when thrust is needed most, the precompression below the strakes increases the efficiency of the intake.
While the F-15 was optimized for speed and transsonic agility within the usual angle of attack range, the Su-27 (and MiG-29, which uses the same basic design) are optimized to be flyable over all possible angles of attack which might be encountered in air-to-air combat. The F-15 designers stopped when the planform and intakes were good enough. TsAGI only stopped until they could not improve the design anymore.
Now to your many detail questions:

What is the main difference between these two engine configurations?

There isn't one, it comes down to details. Both designs support long, afterburning engines, show little yaw when one engine fails and the intakes allow Mach 2+ speeds. The details are less sideslip susceptibility in case of the F-15, because the fuselage helps to adjust airflow, and better high angle of attack performance in case of the Su-27.

What are the differences between planes that have the intakes below
  the cockpit as compared to those who have them on the sides?

Again, the main difference is in off-design performance.

What are the aerodynamic differences?

Now I run the risk of repeating myself. One is better in yaw, the other in pitch. You may decide for yourself wich is more helpful in air combat.

How does this affect the speed/radar signature/maneuverability od the
  aircraft?

This are actually three questions, wrapped into one. In speed the F-15 intake has a small advantage if the greater freedom in adjusting intake geometry to Mach number is taken advantage of. This means that the upper lip can be adjusted, not only the lower lip and the ramps inside, as is the case for the Su-27 intake.
For radar signature, both designs are a poor choice. They are basically corner reflectors, just like the vertical tails. You can see that stealth was no consideration in both designs.
For manoeuvrability, it is the wing planform that counts most. Here the Su-27 wins hands down.

Thanks for the reply, you've explained everything very well

By the way, the two planes I used were just examples that came to mind. There's plenty of other planes with these two configs I could have mentioned, like the F16, the Eurofighter, and the j10 compared to the Dassault Rafale,  the F22 or the F35

@Snippy also keep in mind that it's a matter of engine placement. the engines on the Su-27 have a far larger gap between them than those on the F-15, so to create a straight air duct the intakes need to be further apart.


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How do I know which airports have ILS and for which runways?
I have been into flying for years but something I can't figure out is how do I, as a pilot, know if an airport I am going to has ILS, which runways would have it and why do only some have it but the other side of the same runway does not?  (I.e. RWY 9 has ILS but 27 does not and they use same frequency.) Do I have to look for something specific like localizer vs localizer DME etc.?

There are published instrument approach procedures for all airports served by an instrument approach.  These are commonly referred to as Approach Plates.  (In paper form). Your local pilot shop should have them, or you can order online.
Just look in the section for the airport you are going to and all the available approaches will be there.  Browse to the ones for the runway in use, and choose one that matches your equipment capabilities.  That’s the one you should request with ATC.  (After you get your instrument rating of course!)
If you have a tablet EFB application and the appropriate subscription they can be brought up on your device.
Your question about ILS glide slope not being available on the reciprocal runway has probably been answered before, but the best answer is because it requires a separate transmitter, which costs more money, and needs to be justified based on need and usage.  (I.e. Perhaps the runway without GS is favored by winds when weather is typically clear...)

It should be noted that the approach plates can usually be found at somewhere on the internet, but to actually fly the approach, you are legally required to get them from an official source, and have the latest update (so that it is clear who is obliged to keep them up to date and liable if they are not).

That much is obvious, and comes with the training.

A good place to start getting the info you seek is The Airport/Facilities Directory and NOTAMS give you the actual availability on a day-to-day basis.
Some RWYs have a Localiser BackCourse approach - LOC BC RWXX;
If RW 9 has an ILS, the same Localizer has a Back Course (BC), that lies on RW 27 Approach centerline. Every Localizer has a back course. Obviously it will have the same frequency of the reciprocal ILS as it's the same transmission.
A BC does not constitute an ILS approach, it is a non-ILS approach, or in other terminology it is a non-precision approach. It has no vertical guidance. Minimums therefore would be non-precision.
Here is a  chart for a RW08 ILS, and below that, it's reciprocal RW26 LOC BC:

Another option that you may be looking for, is the "Circle to Land" where you would get a clearance like " Cleared for the ILS Approach 09, Circle To Land 27".
Both the above come with their caveats such as, but not limited to:

BC - procedures/systems to eliminate reverse-sensing of the Localiser deviation bar or localiser 'diamond' during BC approach. Generally, on current generation big jets, as long as the FC (Front Course) of the ILS is set while flying the BC the sensing will be correct while flying the BC chosen from the FMC DATABASE by name. This maybe counter-intuitive to the set-up/flying of a VOR course. In some airplanes the Back Course is set and a BC 'button' is used to ensure correct sensing. You need to check with the manuals and Company procedures.
Circling - setting of Circling Altitude instead of the ILS Decision Altitude as the Decision point by which you have adequate visual reference to continue or go-around.
Circling - may need FAA approval/acceptance as a permitted procedure.

Unless you've already been regular with these procedures, there's never enough prep/ practice you can do.

If you are in the UK, the aerodrome plates and information can be downloaded from NATS at this site It's also available in hard copy in publications such as this

You can easily find out if you are flying in the United States. First, go to SkyVector Airports. Type in the ICAO of the airport you wish to fly to. Then scroll down quite a bit. You fill wind lots of charts. You want the IAP charts. If you see a chart with "ILS" in it's title, for example, "ILS OR LOC RWY 25R", that's what you want. Click on it.
These charts are called approach plates. I won't go too deep into them, because it doesn't seem like you know what they are, hence you wouldn't know how to read one.
Here is an example chart for KLAX ILS 25R approach. In the top right, it says the runway, the airport, and the approach type (ILS or LOC). In the top left, it says the ILS frequency, and just to the right, the runway heading. On the very bottom, there's a diagram of the glidepath. It lists the FAF, which is a "X" symbol with wide edges. This is the altitude you want to intercept the glideslope at.
This should help you start out. But I recommend learning how to read IAP's because they come very useful regarding instrument approaches.

If you are trying to find an easy way to locate ILS approaches in your intended area of flight while flight planning, you might try using web tools such as SkyVector. Tapping on any point on the sectional or chart you are using will bring up a list of points of interest. Tapping on an airport name will bring up a list of Instrument Procedures for that airport. It will be easy to find ILSs from there. In the cockpit, where internet access will be sparse, a dedicated tablet app like ForeFlight will do similarly.


text:
Why does my wind tunnel experiment give two different stall angles of attack?
When I increase the angle of attack from 0 to 20 the stall begins at 18 deg.
When I decrease the angle of attack from 20 to 0 the stall ends at 13 deg.
Why the difference and what value (13 or 18 deg) should I use as the stall angle?

From pilot's point of view, the AoA at which the stall begins is the one that matters. During stall recovery procedure the AoA is reduced dramatically, so the difference you mention matters very little. Academically speaking things might be different.

@Jpe61 what if a pilot fully stalls his airplane? Surely then it would matter?

I don't see how. At AoA above 20 degrees, the wing will be fully stalled, below that it is not stalled. If the case is such that lift will be recovered at 13 degrees, then that's how far you have to "push" the plane (or wings)

That is called hysteresis. Quite normal and grows with the speed of your AoA change.

This is called stall hysteresis. You have two different situations and the flow reacts differently in each of them.
When increasing the AOA
The flow is attached to the wing and the boundary layer is resisting the adverse pressure gradient as much as possible. At some point the flow detach from your profile and you have stalled let's say at 18°. At this point a huge recirculation bubble appears on the succion side of the airfoil.
Decreasing AOA / recovery from the stall
This recirculation bubble represents an area where the average flow speed is close to 0. Looking from the outside, for the free stream flow coming at your wing it looks like you have a new airfoil profile which is made from the old airfoil and the recirculation bubble. Most of the time this recirculation zone extend far beyond the trailing edge of the actual profile, reducing thus the overall aspect ratio (thickness/chord) of the profile. Slimmer profiles have less tolerance to stall and lower stall AOA thus explaining why your recovery only comes when the AOA goes below 13°.
Once the flow is reattached, you are back to the first configuration and you can go back up to the initial stall angle 18°.
Your stall angle is thus 18° but if you are in an airplane it means you'll have to lower the nose below 13° of AOA to recover.
There's an excelent thesis on this subject here from which this picture is taken showing the hysteresis phenomenon.

"slimmer profile"?

Extending the recirculation beyond the TE would reduce aspect ratio.  You might make it clearer that it also increases thickness to chord ratio.  You answer is very good in that it explains that the recirculation bubble must be broken to reattach flow.  Reattachment may be time, as well as angle dependent.  I would try a slower (and faster)  recovery (in the wind tunnel) to see if this affects the reattachment angle. (keeping in mind, in real life, once the plane starts to sink, AOA goes up, recovery should be ASAP).  The recirc bubble has energy, which may account for its resistance.

Your right the aspect ratio is reduced as the bubble increases artificially the chord. Thickness and most importantly the Leading Edge radius is not much impacted by the recirculation bubble, and that's one of the main factor for stall characteristic. The sharper the radius the sonner the stall. By increasing the chord without changing radius you reduse stall AOA. In real life application some dymanics phenomenon appears leading to higher possible AOA before stall and faster recovery but you don't ofter see them in wind tunnel as they are fast transient behaviors that are hard to measure.

That sounds quite nasty to recover from. Is it common in real aircraft?

Not really, as you can see the difference in this case is only 5°, you still have a 13° nose up attitude when the profile recover. Wherase in real life the instant reaction you have to a stall is to release some pressure on the stick and let the nose drop, 5 degree is quite fast to reach.

Furthermore don't forget that stalling doesn't mean instant 0 lift, but rather that your glide ratio drops because of extreme increase in drag and somewhat small decrease on lift depending on the profile. But the airplane doesn't just fall of the sky. You just need to manage your airspeed to ensure your not making the situation worse. And the recovery is quite smooth for a symmetric stall.

yeah, stall is when increasing AoA decreases lift, rather than increase

Note that hysteresis is the name for the general phenomena of the on value being different from the off value. Your heater turns on when the room goes below 18 degrees but turns off when it goes above 21 degrees - that's hysteresis. Your car steering has "play" where it doesn't turn if you move your steering wheel a small amount - that's hysteresis.

Thanks a lot @MaximEck !
You scratched my itchy one.


text:
Is Cessna 150 with incorrectly marked ASI airworthy?
I've looked a bit at the CFRs trying to determine this for sure, but haven't found a clear answer..
One of the Cessna 150s that I rent from the local FBO had it's airspeed indicator swapped out four or five months ago..  the new indicator, in addition to having the low end of the speed range super clumped together so it's difficult to see the accurate reading near the stall speed, is clearly MARKED incorrectly for the airplane that it's in.  The most obvious example is the white arc -- on the ASI that they installed, the top of the white arc is at 80mph, when this Cessna 150M should have the top of the white arc up closer to 93mph.
I know it's not a super huge difference, and I feel that I can fly the airplane safely, but it made me wonder whether it's airworthy with such an obviously incorrectly marked ASI in it.
Thanks!

At least it's on the safe side for your flaps... I have no idea about the regulation but it is definitely weird.

80 knots is 92mph. Perhaps the units have been confused?

@Pondlife That was my first thought when I first hopped in the aircraft and saw it, but nope, it's mph on the outside and knots on the inside, and the top of the white arc corresponds to 80mph..  I unfortunately don't have a picture of the instrument handy, but I did verify units.

Take a look at the equipment list of the Cessna 150.  There are part numbers for every piece of equipment installed.  If the part numbers do not match, then the airplane does not comply with its type certificate data sheet and is not airworthy.  Take a look in the maintenance manuals and find the part numbers.  If the rental FBO refuses to let you see those manuals find a different FBO to rent from.
Unfortunately, that is not the whole story.  There are also other ways for this to be an airworthy airplane:

PMA part.  If the new airspeed indicator has been approved as a direct replacement parts manufactured approved part, it can go in along with the equipment necessary to make it work.  I doubt this is the case as the part would have to be FAA approved for that airplane.  The most common application of a PMA approved part is the installation of LED bulbs for incandescent bulbs.

STC.  The airplane has a supplemental type certificate that modifies the airplane in such a way the new airspeed indicator markings are required for the STC.


text:
Is there any advantage to having both wings integrated into a single wing unit, rather than being attached separately to the fuselage?
if I have a wing, which is split in the middle of it and attached at each side of the aircraft (like in any commercial aircraft today), I get a bending moment at the root of the wing.
What if I have an continuous wing (box) like an oblique wing on the top of the fuselage? A friend of mine says, that this way the wing itself would carry its bending moments. How can I imagine this? Is this just like a beam? Does anybody has some papers about this?

does this answer your question? https://aviation.stackexchange.com/q/3428/1467 https://aviation.stackexchange.com/q/52092/1467

you mean like this?

I think your understanding is flawed. Every commercial aircraft I can think of has a single wing structure from wingtip to wingtip. The main spar either passes through the fuselage below the cabin floor, or above the cabin roof.

@CatchAsCatchCan, the wings are, at least for airliners, definitely manufactured separately, as you can see on the first image here. Yes, there is a structure inside the fuselage that is direct continuation of the wing and carries the load, but the overall structure is riveted or bolted from three parts: the left wing, centre section embedded in fuselage, and right wing.

I am not really sure what you are looking for. There isn't much difference between structure joined from multiple pieces and one build from one piece.

The bending moment is produced by the lift generated by the wings and the weight of the fuselage in the middle, or on the ground the weight of the wings and the support (gear) mounted on the fuselage or fairly close to it. So it is always there.
The only choice you have is how to build the structure to carry that load. You can:

Have a central spar, a solid beam that carries the load, and unstressed or lightly stressed skin. That's how all the early planes with fabric-covered wings and fuselage were built.
Have a hollow wing with stressed skin supported by mesh of ribs and longerons. That's how most aircraft are made today. You have tension load on the bottom and compression load on the top and the centre is not doing much, so not having it there makes a lighter structure.
Anything in between, with solid spar, but some load carried by the skin.

Independently of that, you can

Build the structure in one piece and and attach the fuselage to it (from above, below or build it around).
Build the structure in several pieces and join them with rivets, bolts or glue.

In either case the structure is continuous through the fuselage. The fuselage walls would have no chance of handling the load if you didn't have any connecting structure inside and would bend easily. The only difference is whether it is joined from multiple pieces or not.


text:
Why do drones look different from common airplanes?
In this video is shown Top 5 Military Drone. As we may see, the shape looks different than usual airplanes. My concern is especially with the tail. Normally we know that the tail is vertical. But from those 5, the tails are V-shaped or inverse-V.
I know this is probably a trivial thing for some of you. But that is quite important, as that way is used in most pioneer drones.

A couple of related questions on V-tails: What are the advantages and disadvantages of ruddervators? and What is the difference between the V-shape tail and the straight tail on the Beechcraft Bonanza?

dears, apologize for the duplicate posting. i do don't intent to do so. i have search before i asked this question, especially the articles which shown during writing the question. later i will be more careful to avoid such mistake.

The most obvious difference between a drone or UAV or UCAV, and a manned aircraft is that it has no pilot, and therefore no cockpit structure. In practical terms this means that the minimum cross sectional area of the fuselage is potentially smaller, and the aircraft can be smaller overall than a manned aircraft with similar range/payload capability. In general terms, the smaller the aircraft, the greater the significance of the pilot, ejection seat and cockpit structure as a percentage of the takeoff weight, and the greater the impact they will have on the overall structural design of the aircraft.

If the reason is due to no pilot, the the "head" should be same size with the fuselage. But as we may see, some of them have bulde on their head, room which supposed to be place of pilot. But actually my concern is more to the tail which the shape is V or inverted-V shape. Why not like common airplane?

The Beechcraft Bonanza is one classic light aircraft design with a V tail. Replacing three control surfaces with two saves weight.

Sometimes an inverse-V tail shape is used to protect a pusher propeller from striking the ground.
Many drones have high-aspect ratio wings (long and narrow, like a sailplane) for maximum efficiency and endurance, at some cost to maneuverability.

I can understand if it is intended to protect the propeller from striking the ground. Yes, I have guess so, too. But my question is, why V-shaped or inverted-V shape? V-shape means, there are two tails rather than only one. I have more concern about the tail shape.

What's wrong with the V-tail? Bonanza had a great run of V-tail airplanes starting way back in 1947, and now the FS50 single engine jet from Cirrus is a V-tail. I don't understand what your great concern is.


text:
May an airline replace an airliner's engines without the aircraft manufacturer's involvement?
Around a year ago in our country, there was an advertisement on TV regarding an airliner's program to modernize their airplanes' power plants. This airline has various types of Airbus and Boeing aircraft.
I am not sure whether all the airplanes are using the same power plant brand or not. The advertisement shows that one power plant's manufacturer is GE. So I am not sure what is the meaning of "modernization" in their advertisement regarding the power plant. But instinctively, that should be to replace it with a newer, better version.
So my question is, does the airplane manufacturer allow the airline to replace their own power plants without the airplane manufacturer's involvement?

If the airline owns their airplanes outright, then they don't need permission per-se from the manufacturer, but the new engine would have to be approved by the manufacturer for that type of plane. So the airline couldn't just pick some type of jet engine & decide that they're going to figure out how to mate it to their jets; if that combination hasn't already been tested & proven by the manufacturer, it would void the manufacturer's certifications and render the aircraft un-airworthy. So nobody goes that route.
On the other hand, if the airline leases their jets, they can only do what the owner approves.


text:
Would an ASTERIX decoder be "radar data processing" or "surveillance data processing"?
I am not an air traffic controller, I am a software engineer. I developed an ASTERIX decoder, the application will just extract all the information and save it in a text file.
I am just wondering how we can make use of the application in a real system.
Is that what we call Radar Data Processing or Surveillance Data Processing?
Edit:
I know that my question was ambiguous.So, I will try to clarify it further.
Is the information extracted from the ASTERIX messages useful for the Controller to conduct his work ?

Hi user38218!  I've edited your question to better clarify what I think you're asking.  If this isn't the intention of your post, please feel free to revert it.

I'm not sure if this is easy. Usually companies providing ATC/ATM software provide the ASTERIX parser as well. Last year EUROCONTROL organised a hackathon with this subject. Not sure if the parsers created by the teams were actually used in production.

Stelios Adamantidis So, the parser alone is not useful in a real system?

You can't call it "useless" but neither standalone. It's part of the system. Comparing it to CWP (controller working position) or FDPS (Flight Data Processing System) then yes it's a small chip of a bigger mosaic.

Stelios Adamantidis Awesome !! thank you, I just needed to know how far i am from making a complete system.

After you've edited your question and complementary to what DL wrote, I will answer the

Is the information extracted from the ASTERIX messages useful for the
  Controller to conduct his work?

question:
No in the modern ATC-ATM system it's not. I will consider the "regular" ATCO and not other supportive (but equally important) positions like for example flow controllers that need supplementary systems. So an executive ATCO will need:

Flight data processing. Including complex tasks like trajectory prediction, time estimation etc
Radar data processing. Part of it is the ASTERIX data parsing
Safety nets. That is STCA, MTCD, MSAW, RAM, CLAM and maybe I've missed something. See below for explanations
Weather data. For obvious reasons.
Current AIRAC information. Airways, fixes, navaids, sectors, military areas, coastline, the whole nine yards.
Voice communications. With complex functionality like recording and frequency coupling.
Fusion of all the above in a nice application and UI, usually called CWP. It's the "RADAR screen" that provides the controller with the current situation, and allows them to provide input and change a flight's status. Pretty complex and demanding application.

As you can see, and as I've already commented, ASTERIX parser is a small chip of a bigger mosaic.

STCA: Short Term Conflict Alert. The most important I would dare to say. If there is an outage, you might find yourself with a ticket on hand but unable to fly for several hours.
MTCD: Medium Term Conflict Detection.
MSAW: Minimum Safe Altitude Warning.
RAM: Route Adherence Monitoring.
CLAM: Cleared Level Adherence Monitoring.

Stelios Adamantidis, it's an amazing and a complete answer for me, Thank you very much.

@user38218 Happy to help

You would call this surveillance data processing, but typically surveillance data processing involves much more than decoding ASTERIX.
ASTERIX has many formats, not only radar but also multilateration, ADS-B, tracker output etc, hence the more generic term surveillance is used in lieu of radar.

DeltaLima So, the parser is just a tiny part of the whole Surveillance data processing.


text:
Is there any class G airspace that extends to 14,500 MSL?
The U.S. Aeronautical Information Manual, part 3−2−6, lists a variety of airspace areas which may be designated type E.  From reading this section, I get the impression that "typical" class E airspace consists of regions near non-towered airports, plus everything from 14,500' MSL to 18,000' MSL.
The word on the street, however, is that this is not an accurate picture: In reality, class E airspace typically goes all the way from 1,200' AGL to 18,000' MSL, with dips down to 700' AGL around non-towered airports.  I.e. apart from a thin layer of class G airspace near the ground, almost all airspace away from towered airports is class E.  This is hard to notice on sectionals, since the only place it is mentioned is in the legend, where there is a footnote stating "Class E Airspace exists at 1,200' AGL unless otherwise designated as shown above."  I gather this widespread sort of class E airspace falls under the provisions listed in AIM 3-2-6e4 and 3-2-6e5.
So I have two questions regarding this:

Is there anywhere in the Coterminous U.S. where class G airspace extends up to 14,500' MSL?  (Excluding the trivial case of mountainous terrain above 13,000' MSL; c.f. AIM 3-2-6d1b.)
Since the existence of class E airspace from 1,200' MSL upwards is so ubiquitous, why is this not codified like the 14,500' rule is?

The second question is not answered there, we can edit this question to be not a duplicate

@Federico I tried making an edit as you suggest, but I couldn't make the second half stand alone as a question. Maybe the OP could clarify what doubts remain after reading the duplicate, and get the question reopened that way.

@DanHulme I'm afraid your edit got lost somehow

@Federico No, I threw away the edit because I couldn't make it work.

Historically there was much more uncontrolled airspace in CONUS. There is less but it exists. 14500 is the old continental control area, sometimes called the continental control shelf.  It was designed with the highest natural obstruction in CONUS in mind.
In uncontrolled airspace IFR operations could be conducted without ATC involvement.  I used to do this frequently.
The idea was that in the Continental Control Area, IFR ops were controlled.
For the second question, some Class G exists because there is inadequate service coverage and traffic density and the blanket classification to Class E is inappropriate.


text:
What does "climb to FL300" mean?
If you are flying at FL275 and the control center tells you to climb to FL300, what does that mean and what does the pilot have to do to meet that direction from the ATC?

Could you clarify what exactly is unclear to you? Are you asking about the minimum rate of climb to comply with the instruction?

Does this answer your question? What is the difference between "flight level" and "altitude"?

This could result in duplicate answers of this question since the question seems to be based on a missing fundamental.
https://aviation.stackexchange.com/questions/13204/what-is-the-difference-between-flight-level-and-altitude

It means that the pilot must climb the aircraft from FL275 (27500 feet) up to FL300 (30000 feet) and then continue flying at that level. The pilot will read back the instruction to ATC, and then do it.

And of course maintains FL300 when reaching

@pcfreakxx Fair point :D Edited


text:
Does wearing glasses mean you automatically meet the first class medical requirements?
I have been wearing glasses for a very long time. If you wear permanent eyeglasses do you automatically meet the FAA first class medical vision requirements?

Do the downvoters care to explain?  This looks like a perfectly legitimate question to me.  +1

The first class medical vision requirements are in 14 CFR 67.103 (emphasis mine):

Eye standards for a first-class airman medical certificate are:
(a) Distant visual acuity of 20/20 or better in each eye separately,
  with or without corrective lenses. If corrective lenses (spectacles or contact lenses) are necessary for 20/20 vision, the
  person may be eligible only on the condition that corrective lenses
  are worn while exercising the privileges of an airman certificate.
(b) Near vision of 20/40 or better, Snellen equivalent, at 16 inches
  in each eye separately, with or without corrective lenses. If age
  50 or older, near vision of 20/40 or better, Snellen equivalent, at
  both 16 inches and 32 inches in each eye separately, with or without
  corrective lenses.

In other words, the FAA doesn't care if you wear glasses or not as long as you meet the vision standards. If you can't meet those standards even with glasses (or contact lenses), then you won't be able to get a first class medical.

Certainly not.  Eyeglasses can't fix everything.  Some people have very poor vision even after correction with glasses.  One example out of many, would be someone suffering from macular degeneration.

Right. Or, someone whose prescription has changed. But, they have not changed their glasses, yet.

I am wearing glasses with significant difference between the eyes. With the difference serious enough, putting fully correcting glasses is not possible for both eyes, because it screws up the linearity perception. Straight curves look bent. Not very good for a pilot while you can close one eye and then another can do alone, just without ability to percept the distance that anyway does not reach much beyond the nose of the aircraft.
In any case, a compromise must be made because of this difference, and when I wear glasses, my vision is not fully corrected.
However contact lenses are worn much closer to the eye and do not have this problem. My eyes can be fully adjusted to the perfect vision with the help of two different contact lenses (-2.0 and -6.0).
Hence I think just glasses may not be sufficient (even if they could), but probably contact lenses would work for much wider range of cases. There are also other ways in these days to correct the vision.
I wanted to be a pilot in the past. I have never attempted, because I was deeply convinced my eyes will not permit. Talk seriously with the doctor. Do not repeat my mistake by deciding negatively on your own.

Your vision has to be corrected to 20/20 or something close to it with the glasses on.  I believe you are also required to keep a spare set available.


text:
Why doesn't a radar-equipped Tower say "radar contact"?
Most/all of the control towers in my area have radar displays, and I know from visits that it shows all the same things as in TRACON miles away--even aircraft on the ground.  I hear them occasionally tell both VFR and IFR folks to reset incorrect codes, so they're clearly looking at (and presumably using) the radar display, even in VMC.
So why don't they say "radar contact" like TRACON does?  It seems a little odd that you get a squawk from Clearance Delivery, and Tower checks the literal radar contact on their screen to make sure you got it right, but then you don't hear "radar contact" until talking to Departure.
Also, some busy airports will assign squawk codes to inbound VFR aircraft coming in directly rather than via Approach, but they don't say "radar contact" then either.  This seems even weirder since in that case nobody else ever will--yet you're obviously a radar contact on their screen, otherwise what was the point of giving you the code?

I work at a Class C. For the most part calling "radar contact" is a radar function, but I will do it if, for example, someone will be circling over the city for a while (i.e. not just in the traffic pattern) and will remain in my (Local Control's) airspace.

From the ATC Orders 3-1-9(b)(4):

Unless otherwise authorized, tower radar displays are intended to be
  an aid to local controllers in meeting their responsibilities to the
  aircraft operating on the runways or within the surface area. They are
  not intended to provide radar benefits to pilots except for those
  accrued through a more efficient and effective local control position.
  In addition, local controllers at nonapproach control towers must
  devote the majority of their time to visually scanning the runways and
  local area; an assurance of continued positive radar identification
  could place distracting and operationally inefficient requirements
  upon the local controller. Therefore, since the requirements of para
  5−3−1, Application, cannot be assured, the radar functions prescribed
  above are not considered to be radar services and pilots should not be
  advised of being in “radar contact.”

See the 7210.3 10–5–3a which does permit local controllers who work at an up/down facility to use certified tower radar displays for "any terminal radar function."


text:
Can gusts be reported as lower than wind speed?

KADS 072350Z 31030G20KT 13SM SKC 24/02 A2980

I’ve never seen a negative gust factor before. Is that a real thing (and if so, what does it mean), or did someone just make a typo?

WMO standard defines a gust as the maximum wind speed exceeding the "mean speed" by 5 m/s (10 knots) during the 10-minute interval. With this definition, I would never expect to see a negative gust factor.
However, the FAA defines it differently (FMH-1):

5.4.3 Wind Speed.
The wind speed shall be determined by averaging the speed over a 2-minute period.
5.4.4 Wind Gust and Squall.
The wind speed data for the most recent 10 minutes shall be examined to evaluate the
occurrence of gusts or squalls. Gusts are indicated by rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls.

Thus, by my interpretation, a U.S. airport METAR can report gust speeds below the mean reported wind speed since it only requires a variation of 10 knots, not an exceedance of 10 knots.
However, reading further in the same document:

5.6 Summary of Wind Observing and Reporting Standards
Wind speed: 2-minute average speed in knots is reported.
Wind gust: The maximum instantaneous speed in knots in the past 10 minutes is reported.

It seems impossible to have a 2-minute average speed which is higher than the maximum instantaneous speed over the past 10 minutes. So following that, it would seem to indicate an error in the measuring or reporting equipment.

FAA definition seems reasonable, eg. if you have a constant 30 kts headwind that occasionally drops to 0 for a few seconds, that would be important to know

Updated with additional info. I think the definition is somewhat incongruous with the reporting standards.

It doesn’t say “AUTO”, and the tower should have been open at that time, so my money is on human (rather than equipment) error.

I would say must be a typo, or a non-standard report.
ICAO defines gust in Appendix 3,section 4.1.5.2 c) as an increase of mean reported speed by 10kts or more

That is not the definition of gust. Per the document linked, that is a criteria used for determining when to issue a SPECI METAR.

Sorry, wrong copy+paste inserted wrong link. Edited and corrected right away, but internet is fast...see link now

Gusts lower than the posted wind speed will never be posted on the METAR in the US. By definition per the FAA, the wind speed will be posted as a mean average. Where as the gust will be posted as the maximum wind speed during that time period. You calculate the gust factor by subtracting the mean average from the maximum wind speeds. Since the maximum of anything will be greater than its average, there can never be a negative gust factor.
Another point to make is that since the wind speed posted is a mean average and the gust posted is the maximum, the gust factor works in roughly both directions from the wind speed. In the case of winds reported as 31030G20KT, this would make me believe it to be a typo. Or, the straight line wind gusts were strong enough to temporarily blow in the opposite direction. The question would be why the METAR does not show that as the wind shifting between the directions.

5.4.3 Wind Speed.
The wind speed shall be determined by averaging the speed over a 2-minute period. At designated stations, Table 5-1 shall be used to estimate wind speeds when instruments are out of service or the wind speed is below the starting speed of the anemometer in use.
5.4.4 Wind Gust and Squall.
The wind speed data for the most recent 10 minutes shall be examined to evaluate the occurrence of gusts or squalls. Gusts are indicated by rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. Squalls are indicated by a sudden onset of wind where the speed increases by at least 16 knots and is sustained at 22 knots or more for at least a minute. The speed of a gust or a squall shall be the maximum instantaneous wind speed.
5.4.5 Peak Wind Speed.
Peak wind data shall be determined with wind speed recorders. The peak wind speed shall be the maximum instantaneous speed measured since the last routine METAR.

Never? I posted one in the Q.

Yes, that would make me think it was a typo. Or, winds gusts so strong that it blew in the exact opposite direction without shifting through the other directions. Even though the winds have been  past two or three days, I would vote for typo. Would it be possible for you to post the source of the METAR (not the ADS ATIS, but the service you used to receive it)? Maybe it was a transcription error and is different from other sources.

@StephenS - Nevermind. I pulled the historic METARs from the Aviation Weather Center. It appears to be a definite anomaly.    KADS 080047Z 28009G16KT 10SM SKC 23/01 A2983.
KADS 072350Z 31030G20KT 13SM SKC 24/02 A2980.
KADS 072252Z 28015G23KT 13SM SKC 24/02 A2980.
KADS 072147Z 29014G25KT 10SM SKC 25/01 A2979.
KADS 072047Z 30014G27KT 10SM SKC 25/M01 A2980.
KADS 071949Z 30015G23KT 13SM SKC 25/00 A2982.
KADS 071848Z 29013G24KT 13SM SKC 22/03 A2985.
KADS 071747Z 30014G25KT 10SM SKC 21/04 A2986.
KADS 071650Z 32014G20KT 10SM SKC 20/05 A2986.

@StephenS - I wish Airpark Dallas had a METAR. I doubt the guys I know there would have been at the airport at that time for an on the ground POV. But, neither Mesquite nor McKinney shows a similar anomaly.    KTKI 072353Z 29010G19KT 10SM CLR 23/04 A2979 RMK AO2 PK WND 27026/2334 SLP086 T02280044 10244 20200 52002.    KHQZ 072350Z 27016G25KT 10SM CLR 23/02 A2981

I don’t see anything similar at KDAL, KDFW or KDTO either. My first thought was human error, but I wanted to check in case there was some weird rule I wasn’t aware of.


text:
Can I act as SIC with these specific type ratings?
Can I act as SIC on a part 91 ferry flight, if I hold...

a DC-9 type rating and the flight is in an MD-80?
a B-737 type rating, can I act as SIC on a B-737NG?

Part 91 ferry flights

Welcome to aviation..SE! If you're new to the site, the [tour] might be helpful.

The single B-737 type rating includes all variants of it, from the -100 through the Max; if you were typed in a -200, you have the type, so there is nothing else required in that regard to be Second In Command (SIC) on a 737 NG. (Source... my experience, having flown the -200, classics, NG's, and the Max, all with the one "B-737" type on my certificate.)
The DC-9 family is similar; I don't think there is a separate type for the MD-80.
That all said, there are other requirements pertaining to recency of experience and training. The other answer by @wbeard52 covered these. The pilot would also need a current medical. But as far as required ratings, those mentioned in the original question are sufficient.

If you have a PIC type rating on any aircraft requiring a type rating allows the pilot to act as both PIC and SIC... in most cases.
Depending on your Part 121/135 companies training program, there may be a requirement for specific SIC flight training just like there might be a specific requirement for left and right seat flight training.
Under Part 91, there is no specific requirement to have specific flight training for either duty or pilot seat.
To act as an SIC, FAR §61.55 comes into play:

§61.55   Second-in-command qualifications.

(a) A person may serve as a second-in-command of an aircraft type certificated for more than one required pilot flight crewmember or in operations requiring a second-in-command pilot flight crewmember only if that person holds:

(1) At least a private pilot certificate with the appropriate category and class rating; and
(2) An instrument rating or privilege that applies to the aircraft being flown if the flight is under IFR; and
(3) At least a pilot type rating for the aircraft being flown unless the flight will be conducted as domestic flight operations within the United States airspace.

(b) Except as provided in paragraph (e) of this section, no person may serve as a second-in-command of an aircraft type certificated for more than one required pilot flight crewmember or in operations requiring a second-in-command unless that person has within the previous 12 calendar months:

(1) Become familiar with the following information for the specific type aircraft for which second-in-command privileges are requested—

(i) Operational procedures applicable to the powerplant, equipment, and systems.
(ii) Performance specifications and limitations.
(iii) Normal, abnormal, and emergency operating procedures.
(iv) Flight manual.
(v) Placards and markings.

(2) Except as provided in paragraph (g) of this section, performed and logged pilot time in the type of aircraft or in a flight simulator that represents the type of aircraft for which second-in-command privileges are requested, which includes—

(i) Three takeoffs and three landings to a full stop as the sole manipulator of the flight controls;
(ii) Engine-out procedures and maneuvering with an engine out while executing the duties of pilot in command; and
(iii) Crew resource management training.


text:
How do the fighter jets in air shows color their smoke trails?
At some large military parades or airshows, there will be tiers of fighters arranged neatly. In order to increase the visual effect, white or colored smoke will be sprayed from the tail of the fighters. How is color added to the smoke?

For example the patrouille of france: Under the Alphajet there is a tank called the smoke pod. Inside, two tanks contain oil with a colorant if you want color, or without colorant if you want white.
When the pilot opens one of the valves, the oil flows through a small pipe and exits only at the left reactor. With the heat, around 700 °, it immediately turns into gas and gives this thick smoke.see this(french) http://www.easy-upload.net/fichiers/58456734-63F1-445B-82F7-80213217643D.201872118292.jpeg

That sounds like an answer.

Related

For example for the Patrouille de France under the Alpha Jet there is a tank called the smoke pod. Inside, two tanks contain oil with a colorant if you want color, or without colorant if you want white. When the pilot opens one of the valves, the oil flows through a small pipe and exits only at the left reactor. With the heat, around 700°C, it immediately turns into gas and gives this thick smoke. See this (in French):

Source: pilote-virtuel.com

So... chemtrails?

Nearly :yes but it's not secret...


text:
How much runway does an amphibious Cessna Caravan require for VFR part 135 operations?
I am trying to determine the length required for us to build a simple paved runway for a Cessna Grand Caravan EX Amphibian to depart for water landings and and return (VFR/VMC only, Part 135).
Previous questions about for "runway length required" only refer to Part 135 and Part 91 for Large Transport Category.

Why don't you just ask the owners/operators of the airplanes you are building the runway for?

P.S.  I have performance charts for the wheeled 208 Caravan, if you needed a specific zero wind landing distance, or takeoff and distance needed to clear a 50 obstacle at a given weight, I could give you a number.  But you'd still need to figure out what kind of safety margin you desire.  I think the answer is probably too complex for this forum, but I can tell you that the wheeled Caravans I fly regularly service a 2900' sea level airfield at max weights without issue.  Bigger is always better though, how much space do you have?

The minimum required runway length for a Cessna Caravan is *762m/2500ft. Considering that the Caravan has a stall speed of 60 knots, and for a safety margin, you would approach at 70 knots, this makes sense. Assuming that it slows at a rate of around 1 knot/ 10m, You can do some basic calculations: 70/1, which is 70, resulting in a 700m long runway, plus 62m for a safety margin.
EDIT: But now we're talking about amphibious, so water could help the plane slow down, but at the same time a longer takeoff roll would be required. And it turned out that the website I used wasn't reliable. Sorry about that. Anyways, it is said that an amphibious Cessna Caravan needs a takeoff roll of 2,341 feet/714m. However, the actual requirements force a 3660ft/1116m runway. I didn't get the landing distance required, but I think it's safe to say that the landing would be shorter than the takeoff roll.
*the actual runway length required of a normal caravan is 2,055 feet/ 626m, and you can expect to rotate at 1,160 ft/ 354m.
*Some (incorrect) information was from: http://www.sgl.com/208.html
And more correct info from: https://cessna.txtav.com/en/turboprop/caravan
Please tell me if I should delete the first paragraph.

This seems a little high compared to a C208 POH, which gives 1,795' over a 50' obstacle. I don't know how amphib gear changes the numbers though.

-1 because this relies on several inappropriate assumptions.

@pericynthion: none of my assumptions should be deemed appropriate, but I did forget he was talking about amphibious Caravans, not just Cessna Caravans in general. But I'm still pretty sure someone edited it to amphibious, because I didn't remember that being there.

@pericynthion: pls remove the downvote if I made the correct corrections, and tell me exactly where I went wrong so I can improve.

@Pondlife: That seems to be very odd. I don't know why a POH would have such a dramatic difference, but it is smaller. That still doesn't explain why the stall speeds are the same. Very odd.


text:
What does "wraparound" mean in the context of flight controls?
In the references regarding the flight control (for example in F-16) I see the word "wraparound". For example "Rudder coil wraparound", "IBU pitch wraparound", "IBU lateral wraparound"or "AMUX bus wraparound failure". What does this word mean in this context?

Wraparound is a method used to ensure flight control computer (FLCC) commands are reaching the actuators as they were inteded.
To maintain a desired flight condition FLCC calculates necessary control surface movements. These calculations are translated into control signals that are sent to actuators. These signals are periodically monitored by wraparound loop to verify they match the command originally calculated by FLCC.
This is the quickest (and the only viable) way to verify system integrity, since there is no need to wait for aircraft sensors to verify the plane did what FLCC wanted. Should the wraparound signal not match what FLCC commanded, the control reverts to a backup system.
Without wraparound, faulty signals would lead to incorrect control surface movements, that would in turn lead to corrective action by FLCC, and should the fault in the signal delivery persist, the corrective action would of course be also wrong.
Pilot action to supress these incorrect control outputs would be difficult at best, impossible at worst, since commands given by pilot are delivered through the faulty system. In the case of modern, unstable fighter jets, the worst possible outcome is the most likely one.
A diagram of wraparound arrangement can be seen here: NASA technical paper 2857, page 91
Wraparound is pretty well described in this patent application: Failsafe digital bus to analog protocol converter system

A failsafe avionics interface unit (10) serves as a protocol converter system for translating data for control purposes from a digital communication bus (65) to an analog control channel as an upgrade or interface to an existing analog control system. The avionics interface unit (10) includes digital interface bus logic (101), a digital data processor module (102), an analog interface, and a mode selection circuit (104). Data communicated over the digital interface bus (65) is periodically translated into equivalent analog control signals. For safety purposes, the avionics interface unit (10) ensures the integrity of the system by repetitively looping back or wrapping the digital equivalents of the analog output signals and comparing them to commanded digital control values. The protocol converter system additionally monitors communications over the digital data bus for data continuity. If the difference between a wrapped digital equivalent of an analog output signal and an expected value exceeds tolerable limits or if communication fails, the system disconnects its interface from control using redundant software and hardware and returns control to the analog control system (51).


text:
In a CFD simulation the wingtip vortexes gets reduced/cancelled by means of Wingtip End Plates- if this is true is it then useful?
I am just working on a special kind of wing and I do named it a Transformer Wing.
The transformation is about the wing camber.
The main requirement of the project is that the wing is to be not flexible but be able to reverse the camber within a second.
The choosen specific solution requires that the transformer wings need to be short, rectangular and effective.
Check the idea of my wing on YouTube:

As the wing needs to be short and rectangular then the wingtip vortex will destroy much of the lift produced by the wing due to very low AR.
Therefore my work gets much to be concentrated to understand the wingtip tornado vortex.
As the wing needs to reverse the camber it was not possible to apply any of the existing, well working solutions within aviation, except for End Plates.
It is to be noted that the Wingtips End Plate form used for my wing are dividing the air flow into four smaller vortexes.
The very low pressure caused by the wingtip vortexes is now moved toward leading edge
therefore the lift vector is directed as we do want.
It is possible that we can still improve the form of the end plate in order to prohibit observed turbulence close to trailing edge.
It looks that the End Plates can be compact and add not much to wing span or wingtip weight.
At the same time they are nice-looking and are effective when it comes to aerodynamics.
Right now I find that proposed End Plates improved the CL and L/D (Ok, its only CFD).
Now to my question:
My observation is that the vortexes can cancel each other to some degree as they rotate in same rotational direction (i.e. both are rotating clockwise on the left edge of the wing span) though when they meet then the air speed goes down.
This phenomenon might reduce the dirty air behind sailing vessels and reduce danger for aeroplanes?

Can you post a couple of pictures from your CFD simulation?

Interesting concept, what would be the purpose?

For end plates to be beneficial, the savings in induced drag must outweigh the increase in parasite drag from end plates themselves; possible if the end plates have a thin aerofoil. Also, the savings in induced drag depends on the net induced drag itself, so the end plates might improve the aerodynamics at high Cl (low speeds), but worsen it at low Cl (high speeds).


text:
Which type of chevrons is applied on the B787?
Which type of chevron nozzle was applied on the B787? I'm really confused about whether if it's sawtooth or sine wave.

Strictly speaking, its neither. Chevrons don't resemble either a sawtooth wave or a sine wave in mathematical terms. The closest is that it is a smoothed (modified) saw tooth form.

Image from compositesworld.com
Though the initial research used a serrated nozzle in saw tooth form, the final commercial application differs from it. However, the chevrons are repeatedly noted as having a saw tooth form, by NASA among others:

One of the most recent noise-reducing technologies shepherded through the research process by NASA and now making a difference on commercial jet engines is chevrons.
Chevrons are the sawtooth pattern seen on the trailing edges of some jet engine nozzles.

So, it's a choice between saw tooth and sine wave, its better to go with the former.
GE's patent for the Chevron describes the shape as triangular with qualifications:

... each of said chevrons being triangular in configuration
... said chevrons having a compound concave contour both axially between said bases and apexes and laterally between said trailing edges..

Image from Chevron exhaust nozzle for a gas turbine engine


text:
What are the implications of building a private airfield in the United States?
I've always wondered what it would take to build my own airfield.  I live close enough to an area where this would likely be possible (50 NM radius around Front Royal, Virginia, obviously outside the DC SFRA) and there are a number of private strips in the valleys adjoining mountain range I live near:

Here are the parameters I would consider, which would allow operation of one or more small general aviation aircraft:

Runway width - 50-75 feet
Runway length - 2200-2500 feet.
Runway surface - grass
Buildings - Space for a hangar (converted barn?) and a moderately sized house.

Answered Questions:

What are the legal implications in the United States?  Do you have to get permission from the government to do this?  Is this airspace dependent?  Answered in linked post and this post.
What about permission from neighbors?  I'm going to guess this will be harder to answer, since it likely depends on jurisdiction.  However, if anyone has done this, perhaps they can share their experience in this area.  Somewhat answered in revised post.  Still interested in additional experiences.

Outstanding Questions:

What would it cost to maintain this installation, above and beyond the cost of maintaining any piece of property of this size?  What's included in these costs?
Are you required to pay to have an airfield listed on charts?
Do the parameters I've listed seem reasonable for the requirements I've mentioned?

You have many questions in one. Perhaps focus this question on the regulatory aspects, and ask more questions regarding maintenance costs, runway parameters, etc

Hello, this is a good and interesting question, unfortunately it is too broad for this site's format. After you narrow down the scope, I am sure you will get some great answers.

Welcome! I reduced the scope to the administrative part (you will have to ask a second question for the technical aspects). If you feel I was wrong, you can revert to your initial text using clicking the "edited...." link at the bottom of the question, and then using "rollback". That's a good question!

@simon how do I remove the duplicate tag from this question now that I have edited it?

These are great questions, and I'm surprised that more people haven't offered helpful answers. I'm curious and eager to see when they do. I'd love to have my own runway some day.

This has been somewhat covered in other questions here. You can find the legal requirements in the answer to this question (somewhat of a dupe to this question). There are some notes on security in this question.

What would it cost to maintain this installation, above and beyond the
  cost of maintaining any piece of property of this size? What's
  included in these costs?

For a grass strip you will need a good ride on mower and possibly something to level/press the ground. Maybe some filler if there are any divots etc. But all in all the cost to maintain a strip of grass is pretty cheap.

Are you required to pay to have an airfield listed on charts?

Im not sure of this one but there may be some requirements you need to meet which could cost you money.

Do the parameters I've listed seem reasonable for the requirements
  I've mentioned?

Yes, 22-2500 is more than common, FWIW a bit on the short side but you should have no problem getting your common GA planes in and out of there. Keep in mind that with trees at the end and on either side this could get tight. In reality runways (at least nice paved ones) have a lot of clear space around the immediate area.


text:
What general aviation operators might hire a low time pilot?
I recently obtained my CPL at FTA.
In one of the answers:

The normal progression is this - you can technically get a flying job after 150-200 hours of private training and flying, having achieved your commercial pilot licence (CPL). I say 'technically' because if you only have minimum hours and minimum qualifications you have to look very hard for a job. Most people straight away get an instructor rating, so they can get a job teaching people to fly. Other early jobs include sightseeing flights, parachute flights, and mail flights to remote towns.
Your training will have been in light aircraft, but fortunately Australia has possibly the largest light aircraft industry in the world, so there's lots of jobs in these planes. It's highly unlikely that your first job will be in anything bigger than a 6 seater plane.

Could somebody suggest based on your experience, light aircraft operators willing to hire a 250 hours pilot?
I already sent my resume to a list of GA operators and did not receive any reply. I need some advice on the best approach when trying to get my first job.
Look forward to hearing from you.

I edited your post to add helpful formatting and a link to where you got the quote. Also, see this question for ways to build flight time.

This seems like information that will probably go out of date relatively quickly.

Move to Alaska and start doing whatever airport job you can find.  Make friends.  Eventually you'll get a chance to fly something.

You should clarify which country you are asking about

Sorry, Ben I was referring at Australia as in one of your comment you mentioned that Australia has the largest light aircraft industry in the world. I thought you could suggest some GA operators that might hire low time pilots. Or, better how can  I tackle getting the first job as a 250 hours pilot. Adrian

Getting your instructor certificate is your best bet.
Beyond that, there are jobs out there for traffic watch, banner towing, and flying jump planes for skydivers.  Also glider towing and sightseeing.  Ferry flying is possible, although I'd be careful of any place that would hire you with very few hours -- they may be cutting corners & guys with more time look at the operation & say "no thanks."  Not necessarily, but be cautious with anything that looks "too good to be true."
All of these are typically positions that only have a few, or one, or no openings at a time, and those spots are in pretty high demand.  So persistence and personal contact (not just sending a resume) are probably vital to landing one of these jobs.  The place where you're most likely to have more options is flight instructing; obviously that requires the CFI certificate (or equivalent for outside the US).
Good luck!

I'll only add that if you do encounter a place that seems shady, make sure they arent a "134 and a half" operation that is a commercial operator without a 135 certificate.  Flying for an op like that isn't going to look good when the feds come knocking.

Even flying skydivers is tough these days.  Most insurance companies want 500 total time and 25 in type to fly Cessna 182s and 206s.  Turbines are 1000+ hours.

Nobody can tell you every single operator who might hire you. There are a couple of operators that I personally know have hired low-time pilots, like Merimbula Air Services or Polar Aviation. But what I want to do here is give you some strategies that could help you land your first job:
1) Don't  stop training
Passed the CPL Flight Test? Great! Now do more. Get as many endorsements and ratings as you can - tailwheel, aerobatics, low level etc. Fly as many different types of aircraft as possible, then search for operators who fly those types. And if you can afford it, the holy grail would be to get a MECIR. But a very good-value rating to get is the instructor rating. Needless to say this could get you a job almost anywhere in the country, but it is nevertheless a competitive field.
2) Get schmoozing
The aviation industry in Australia is relatively insular. It is often not just what you know, but who you know. Rub shoulders with as many people as you can - not just pilots but engineers, managers too. Don't burn bridges. Any one of these people might one day have a friend who is expanding their operation and they could recommend you. Your instructors could be friends for life - ask them how they have gotten to where they are.
3) Consider your  approach
Similar to the point above, are you simply sending your CV to random operators? This is often more annoying for them than anything. Pick up the phone (or better yet drop in) for an honest, genuine chat. Even if they haven't advertised, they might have it in the back of their mind that they need another pilot. If you make a good impression the worst that can happen is they will have you in mind next time there is a vacancy.
4) Broaden yourself
I think this is an aspect of pilot recruitment that is often overlooked. Most operators that would hire you are a small business. You are so much  more valuable to them if you can do more than simply fly a plane. Work on your non-technical skills - get some experience in customer service, HR, office administration, or book keeping. Larger operators in particular need more hands in their regulatory/safety management areas - if you are good at policy implementation or technical writing you could be useful here. By selling your non-piloting strengths, might not be flying full-time but it's a door in to the aviation world, and will certainly help your overall career prospects. As an example, I think there's a great opportunity at the moment with the ATSB to be essentially a junior investigator, and all you need is a CPL. You won't be flying in this job but you'll gain so many experiences relevant to a flying career (plus a handsome salary). If you have training in accident investigation larger operators, especially airlines, will love you.
You've picked a difficult profession to crack into, but with patience, persistence and intelligence you'll get there.

If I have an Australian CPL can I fly in Indonesia? How likely is to obtain employment if I have 250 hrs. flight in Indonesia?

@Adrian You should be able to convert your Australian licence to an Indonesian one pretty easily (though the Indonesian DGCA website is difficult to say the least...). You might need to sit an exam or do a flight test but your 250 hours will count. As for job prospects, I'm afraid I can't answer that. It seems not many here are that familiar to the Indonesian industry. There are other aviation-related forums that might be more useful. Best of luck.


text:
Is there a general standard for servo actuators?
It is said in the standard AS94900 that the standard ARP490 should be considered for the actuators of the control surfaces in the aircraft. However, this standard is on servo valves and not servo actuators. is there a specific standard for servo actuators in aviation? or the servo valve of the servo actuator should be tested separately?


text:
Can an ultralight be flown at night or IFR?
In Canada, can an ultralight be flown at night or IFR by a PPL pilot with a night flying or IFR endorsement if the ultralight is equipped for night flying or IFR ( eg. heated pitot tube, nav lights, etc.) and a seatbelt?

"CAR 605.18 No person shall conduct a take-off in a power-driven aircraft for the purpose of IFR flight unless it is equipped with..."

The answer is "yes", unless you add "legally" or "in compliance with the regulations" to the question!

In the US, per 14 CFR Part 103.11, you can not operate an ultralight at night or IFR. You can, however, register it as an aircraft. Which, at that point,it no longer qualifies as an ultralight.

§103.11 Daylight operations.
(a) No person may operate an ultralight
vehicle except between the hours of sunrise and sunset.
(b) Notwithstanding paragraph (a) of this section, ultralight vehicles
may be operated during the twilight periods 30 minutes before official
sunrise and 30 minutes after official sunset or, in Alaska, during the
period of civil twilight as defined in the Air Almanac, if:
(1) The vehicle is equipped with an operating anticollision light
visible for at least 3 statute miles; and
(2) All operations are conducted in uncontrolled airspace.

This question appears to be about Canada, if I understood correctly, so US regulations wouldn't apply.

Just found the following ( Source: Challenger.ca ): Aircraft registered as Ultralights may only be operated in Day VFR conditions. You can operate a Challenger at night or under Instrument Flight Rules if it is registered in the Aeroplane category as an Amateur-Built and if it complies with the lighting, instrumentation and other equipment requirements.


text:
How do airplane designers determine flap deflection angles for flaps of various % wing chords?
How do airplane designers determine flap deflection angles for flap chords of various % wing chords? E.g. flap chord of 30%, 40% or 50% of wing chord.
I understand most flaps' chords are about 25% of the wing chord, but I understand Rutan's Grizzly had a flap chord of 55% of wing chord.
I assume you could use theory to figure this out, but that doesn't mean it works like that in the real world.
Is this information readily available in graph or chart form?
I thought I saw a link in a post on StackExchange re this from Peter Kaempf, but I can't find it.

First with tunnel data or CFD which is later refined in flight test.

@Fred, your edits have cleared this up for me, but I still think you are thinking about this in reverse.  For example, almost every plane I've flown has flap settings in 10 degree increments.  (One is 15 degrees...)  I think the designers prefigure standard settings, then by calculation and test derive the performance obtained.

As a rule of thumb, flap effectiveness (that is lift coefficient change per flap deflection angle or c$_{L\eta}$) is proportional to the square root of the flap's percentage. A more precise formula was derived by Hermann Glauert (search for the name and you will find that elusive answer by me)
What also changes is the hinge moment needed per degree of flap deflection; this, however, changes with the square of the flap's percentage. By trading off effectivity versus force, a designer will find the best flap percentage for each control surface.
Next, wind tunnel data is used for finding the effectiveness over deflection, because this value decreases with higher deflection angles and is hard to catch by CFD because viscous effects are strongest near the trailing edge and need lots of effort to model correctly. The desired control response and trim should be achievable with maximum deflections of below ±15° (the useable range is wider for smaller percentages) and the flight test will reveal whether the calculations were correct.

If by % flap chord you mean the fraction of the wing chord occupied by the undeflected flap, then the bigger the % flap chord, the smaller the angular deflection needed to achieve the same effective camber.
Specific cases depend, of course, on the airfoil, the AoA envelope, unusually large or small flaps, flaps that extend aft, flaps with slots, etc.  That would be more plots and tables than could fit into an answer here.


text:
Do these red stop signs apply to aircraft or only to vehicles?
I mean; do planes also see these signs on their way to runway? Or just cars and other vehicles encounter this stop sign on their service road or interconnection roads that are assigned to them?

No, those signs do not apply to aircraft. They are for vehicles and marks entry to the maneuvering area.

So vehicles can see these marks in the borders of apron right? Because the maneuvering area does not comprise apron.

I mean it will depend on the local airport. But generally speaking, since the apron is not part of the maneuvering area, a vehicle does NOT need clearance from tower to drive on the apron

Yeah, you are right. Now, I see what you did emphasize, thank you! And you are ATC too; I am cadet ATC right now. I would like to communicate with you on social media if you want it too. my Instagram account is written in my profile. Later,

Hey Volkan. I'm not really active on social media, but feel free to drop me a chat on this site

Confirm Mr. Hougaard; later!


text:
Is there a standard international Minimum Obstacle Clearance Altitude (MOCA)?
In Turkey, the Minimum Obstacle Clearance (MOC) in primary areas is 300m; what about other countries and region?

The MOC value you are referring to is related to the en-route phase of an IFR flight, so your statement that it is the lowest altitude a plane can descend to when approaching the runway is wrong. That value depends on the type of approach, aircraft equipment and various other factors. It is not a fixed value shared among different airports. You probably have MOC confused with Minimum Descend Altitude (non-precision approaches) or Decision Altitude (precision approaches).
However, to answer your actual question, 300 metres is an ICAO standard for MOCA (Minimum Obstacle Clearance Altitude) in the primary area for the en-route phase of an IFR flight. So other countries use the same value, unless they have special local rules specifying a different value.
Note than, in mountainous areas, the minimum obstacle clearance applied, depending on terrain elevation, is 450 metres for terrain between 3000 ft and 5000 ft, and 600 metres for terrain higher than 5000 ft.
Minimum Obstacle Clearance Altitude (MOCA) on Skybrary

About your comment and inference on my info; let me explain: actually OCA is the REAL MOC on the last approach (I mean FAF: Final Approach Fix)

In the US the MOCA—Minimum Obstruction Clearance Altitude is 1000' in non-mountainous areas and 2,000' in designated mountainous areas. A map of the areas is contained in 14 CFR PART 95—IFR ALTITUDES. In addition to obstacle clearance the MOCA also ensures reception of VOR signals. Pilots flying off-route e.g GPS direct, are responsible for determining the MOCA for their route.

e) The MOCA assures obstruction clearance on an ATS route, ATS route
  segment, or other direct route, and adequate reception of VOR
  navigation signals within 22 nautical miles of a VOR station used to
  define the route.


text:
What is garbling in the context of radar?
Garbling is a problem known to affect secondary surveillance radar (SSR). What is it and why is it a problem?

Garbling occurs when two aircraft are close enough that their replies overlap, as there is no reliable way to sort them out. Usually this occurs when the aircraft are passing above each other as the radar scans the entire vertical column at once, only rotating horizontally.
The problem is that the controller might not be able to check the aircraft are indeed flying their correct assigned altitudes exactly at the moment when it matters most when they are passing above each other.
Quick Googling reveals e.g. this article with some diagrams of the overlapping signals.
A related problem is “fruit”, which is the squawks triggered by other things than the radar beam (e.g. the interrogations from T-CAS on other aircraft) being mistaken for ones that were, and therefore making the aircraft appear at other place than it really is.
Both issues are mitigated by ADS-B, because there the aircraft broadcasts at semi-random points and includes it's own position, so while the messages may still conflict (like in other transmission protocols), the timing is designed to make it unlikely to happen for several following messages.


text:
What were four objects seen in Flightradar24 over Germany with the callsign TWR?
In Flightradar24 from 290030Z and then for two more hours, there were 4 identical objects over Germany between EDFM and EDDS at altitudes from 600 to 1900 feet, a few knots speed and each changing course more than two times per minute but no trace like if stationary. The distance between the objects was about 20km. They all have the same callsign: "TWR". What are they?

Keep in mind FR24 is essentially a huge number of hobby receivers picking up basically anything transmitted on 1090 MHz and then trying to associate those signals with a known database of flights. It is not always accurate. Many flights are not shown, and sometimes something is shown that does not actually exist

@expeditedescent, or, in this case, apparently on 868 MHz.

Does this answer your question? What is this squawk 7777 target at an altitude of 62,700' over Germany?

Many towers in Germany are equipped with FLARM so that they are electronically visible to FLARM equipped aircraft in the area. This is especially useful for helicopter emergency medical services and law enforcement that operate in urban areas during marginal weather conditions.
The fact that the towers are not always visible on FR24 may have to do with the fact that not all their receivers are equipped with FLARM. If nobody nearby is providing FLARM data to FR24, the towers are not visible on FR24.
The speed shown has to do with the GPS receiver in the FLARM unit; they sometimes detect small speeds, even though the receiver is stationary.

Perhaps the speed is due to tower sway getting picked up by the GPS?


text:
Can you turn off the instrument panel lights?
Do general aviation aircraft generally allow the turning off of the instrument panel lights? By lights I am referring to any screens, bulbs or other devices which shine a light within the cockpit.

This was a factor in the emergency passenger landing of John Wildey. He had no instruments after the sun set because he was unable to find the light switch in the Cessna 172 he was flying.

It seems having a mini MagLite with you can save your day.

It depends.
On my Cherokee, when you turn the navigation lights on you can push the switch up or down. Up gives you bright lights on the panel and down gives you dim lights. There is also an overhead red light that has a sliding door that you can open or close for more or less light. There is one rheostat that controls the lighting in the VOR/LOC indicator.
On my Cessna 210 there are lights in some of the instruments, post lights next to the instruments, and overhead lights. The lights are controlled with two switches and several rheostats. The GPS has independent lighting controls.
The Piper Arrow has two rheostats—one for navigation and radios and one for instrument panel lights. If you turn the navigation lights on there is always some lighting on the radios. The GPS has its own lighting controls.
My friends Piper Dakota has lights for the instruments as well as a light strip along the base of the glare shield that illuminates the entire panel. Controlled by a combination of switches and rheostats.
Older general aviation aircraft have widely varying approaches to nighttime lighting so before you fly at night you need to become familiar with the idiosyncrasies of each one.

There are instrument panel and flood light controls which are equipped with a rheostat so they can either be dimmed or turned off all together.